Membrane filtration technology has been widely used for liquid purification. Polyamide thin-film composite (TFC) membranes efficiently remove small particles and ions, and have been used for water desalination processes, such as nanofiltration (NF) and reverse osmosis (RO).
Fouling can become a problem in membrane filtration processes, even if the feed liquid is pre-treated to remove potential foulants. Fouling is a process that results in a decrease in performance of a membrane, caused by the deposition of suspended or dissolved solids on the external membrane surface, on the membrane pores, or within the membrane pores. To reduce fouling, the surface of the membrane may be chemically cleaned, or the system may be flushed periodically to remove foulants on the membrane surface.
Two principal types of fouling deteriorate membrane performance over time. Organic fouling can be caused by natural organic matters (NOMs) that accumulate on the surface of the filtration membrane, form a thick cake layer, and even block the internal pores of the membrane. Organic fouling can cause severe flux decline and shorten the useful life of filtration membranes. Biofouling caused by bacteria in the feed water can also compromise membrane performance. Bacteria cells can adhere to the membrane surface and form a thick biofilm on the surface that is very difficult to remove.
To effectively maintain membrane performance for extended periods of time, membrane coatings with both antifouling (AF) and antimicrobial (AM) functions are needed.